Order 66 submitting score of 0

It's allowed for low-end players in medium guilds. They have to post a score (even a zero) to qualify for raid rewards. So SOME ppl in their right minds would want to do it.

But you're correct that these are special situations and the vast majority of times a zero is posted it's probably an accident. 

Rather than a warning, I think they could just ban submitting scores of zero above tier zero. If you're just posting bc your teams are so bad you can't do anything but your guild is earning rewards, you can still submit a zero on t0. Those players don't get any advantage out of submitting a zero on t7 instead. People running the higher tiers would be better served not by a warning, but just by disallowing scores of zero entirely. If you really can't score, drop down to a tier where you can.